1. Field of the Invention
The present invention relates generally to implantable devices, such as synthetic vascular grafts and covered stents. More particularly, the present invention is directed to a method of impregnating an implantable device with substances as well as to an implantable device that has been so impregnated.
2. Description of the Related Art
Occlusion of blood vessels reduces or blocks blood flow. During the course of atherosclerosis, for example, growths called plaques develop on the inner walls of the arteries and narrow the bore of the vessels. An embolis, or a moving clot, is more likely to become trapped in a vessel that has been narrowed by plaques. Further, plaques are common sites of thrombus formation. Together, these events increase the risk of heart attacks and strokes.
Traditionally, critically stenosed atherosclerotic vessels have been treated with bypass surgery in which veins removed from the legs, or small arteries removed from the thoracic cavity, are implanted in the affected area to provide alternate routes of blood circulation. More recently, implantable devices, such as synthetic vascular grafts and stents, have been used to treat diseased blood vessels.
Synthetic vascular grafts are macro-porous vessel-like configurations typically made of expanded polytetrafluoroethylene (ePTFE), polyethylene terephthalate (PET), polyurethane (PU), or an absorbable polymer. Grafts made of ePTFE or PET are very non-wetting materials when introduced into an aqueous environment, causing difficulty in impregnating the materials. In addition, grafts made of ePTFE or PET are permanently implanted in the body, while grafts made of an absorbable polymer bioabsorb over time. A graft may be positioned into the host blood vessel as a replacement for a diseased or occluded segment that has been removed. Alternatively, a graft may be sutured to the host vessel at each end so as to form a bypass conduit around a diseased or occluded segment of the host vessel.
Intravascular stents may be permanently or temporarily implanted in narrowing blood vessels. Typically, a vascular catheter, or similar transluminal device, is utilized to carry the stent to the treatment site. The stent is expanded to support, and if desired expand, the diseased portion of the arterial wall. The insertion of a stent into a vessel in which plaque has become brittle over time, however, may cause complications if the stent causes the brittle plaque to break off from the vessel wall and embolize the lumen. A covered stent, in which a graft-like covering is slip-fit onto the stent, may therefore be employed to isolate the brittle plaque from direct contact with the stent, which is rigid.
To treat such damaged vasculature tissue and to help prevent thrombosis and restenosis, there is a need for administering therapeutic substances to the treatment site. To provide an efficacious concentration to the treatment site, systemic administration of the therapeutic substance often produces adverse or toxic side effects for the patient. Local delivery is a highly suitable method of treatment, in that smaller levels of therapeutic substances, as compared to systemic dosages, are concentrated at a specific site. Local delivery produces fewer side effects and achieves more effective results.
One technique for the local delivery of therapeutic substances is through the use of medicated coatings on implantable devices. In addition to providing local delivery capabilities, such a coating protects vessel tissue from injury and helps prevent excessive foreign body reaction that may occur when such a device is implanted.
The present invention provides a method by which implantable devices, including those made of very non-wetting materials, may be impregnated with passive as well as therapeutic substances. An implantable device that has been impregnated with such substances is also provided.
In accordance with one embodiment of the present invention, a method of impregnating an implantable device, such as a vascular graft or a covering adapted to be disposed over a prosthesis, is provided. The method includes an act of providing a substrate having a body and interstices throughout the body, an act of applying a composition containing a first substance and a first fluid to the substrate such that the composition penetrates into the interstices of the body of the substrate, and an act of removing essentially all of the first fluid from the composition within the body of the substrate. The first substance remains within the body of the substrate. An implantable device having a first substance deposited therein in accordance with the above-described method is also provided.
In some embodiments of the method described herein, the first substance is a pre-polymer. In such embodiments, the method further includes the act of causing the pre-polymer to crosslink to form a hydrogel within the body of the substrate. In addition, an implantable device having a hydrogel formed therein in accordance with the method is provided.
In other embodiments of the above-described method, the body of the substrate has a first end, an opposing second end, and a hollow bore extending longitudinally through the body from the first end to the second end. In such embodiments, the method may further include the act of providing a prosthesis and the act of inserting the prosthesis at least partially within the hollow bore of the body of the substrate. In some embodiments, the prosthesis has a plurality of depots formed therein. In such embodiments, the act of providing a prosthesis may further include the act of forming the plurality of depots within the prosthesis. The act of providing a prosthesis may also include the act of depositing a second substance within the plurality of depots. The deposited material may be selected from therapeutic substances, polymeric materials, and radiopaque materials, among other possibilities.
In other embodiments of the above-described method, prior to applying the composition, the method additionally includes an act of applying a second fluid to the substrate. In other embodiments, subsequent to applying the second fluid and prior to applying the composition, the method additionally includes an act of applying a third fluid to the substrate. In still other embodiments, the method additionally includes an act of applying a bridging fluid to the substrate between the otherwise consecutive application of immiscible fluids.
In other embodiments of the above-described method, the composition additionally includes a therapeutic substance. The therapeutic substance is selected from a group of antineoplastic, antimitotic, antiplatelet, anticoagulant, fibrinolytic, thrombin inhibitor, antiinflammatory and antiproliferative, antioxidant, and antiallergic substances, and mixtures thereof.
Also disclosed is an implantable device. The device includes a substrate having a body and interstices within the body. The body has a first end, an opposing second end, and a hollow bore extending longitudinally through the body from the first end to the second end. The device also includes a first substance impregnated within the interstices of the body of the substrate and a prosthesis inserted at least partially within the hollow bore of the body of the substrate. The prosthesis has a plurality of depots formed therein. In some embodiments of the implantable device, the plurality of depots contain a second substance.
These and other aspects of the present invention may be better appreciated in view of the detailed description and drawings of the exemplary embodiments.